WO2011101987A1

WO2011101987A1 - Lithium ion secondary battery and production method for same

Info

Publication number: WO2011101987A1
Application number: PCT/JP2010/052606
Authority: WO
Inventors: 山口　裕之
Original assignee: トヨタ自動車株式会社
Priority date: 2010-02-22
Filing date: 2010-02-22
Publication date: 2011-08-25
Also published as: KR20120109492A; US20120328949A1; JP5534369B2; CN102804475A; KR101368029B1; JPWO2011101987A1

Abstract

Disclosed is a lithium ion secondary battery which is provided with cathode active material containing Mn, and which exhibits improved charge/discharge cycle characteristics. The secondary battery (10) is provided with: a cathode (12) having cathode active material containing manganese; an anode (14) having anode active material; a non-aqueous electrolyte (20) which lies between the cathode (12) and the anode (14); and an acidic-group containing polymer (18) which is disposed between the cathode active material and the anode active material.

Description

Lithium ion secondary battery and manufacturing method thereof

The present invention relates to a lithium ion secondary battery provided with a positive electrode active material containing manganese.

A lithium ion secondary battery includes a positive electrode and a negative electrode that include an active material that reversibly absorbs and releases lithium ions, and an electrolyte that is interposed between the two electrodes, and lithium ions travel between the electrodes. Charge / discharge. Typical positive electrode active materials include lithium transition metal oxides such as lithium cobaltate and lithium nickelate. Typical examples of the negative electrode active material include carbon materials such as graphite.

In Patent Document 1, in a battery using a carbon material for a negative electrode, by covering the carbon particles with an acrylic acid polymer such as acrylonitrile or acrylic ester, characteristics such as initial Coulomb efficiency are suppressed by suppressing the irreversible reaction of the battery. It is described that it can be improved.

Japanese Patent Application Publication No. 8-195197

In recent years, expectations for a positive electrode active material containing manganese (Mn) as a constituent element have increased as an inexpensive positive electrode material. A lithium manganese oxide having a spinel crystal structure (including a composition in which part of Mn is replaced with another metal element) is a typical example of a positive electrode active material containing Mn. However, the positive electrode active material containing Mn has less deterioration due to charge / discharge cycle characteristics of the lithium ion secondary battery constructed using the active material than the positive electrode active material not containing Mn. ) Tended to be low.

Accordingly, an object of the present invention is to improve the charge / discharge cycle characteristics of a lithium ion secondary battery including a positive electrode active material containing Mn.

As one factor causing deterioration of a lithium ion secondary battery including a positive electrode active material containing Mn, divalent Mn derived from the positive electrode active material (for example, trivalent Mn is disproportionated into divalent and tetravalent). It has been pointed out that a high-resistance film may be formed by elution into the electrolytic solution and depositing on the negative electrode. The formation of such a high-resistance film can increase the internal resistance (DC resistance) of the battery and cause a decrease in battery capacity. The present inventor considered that Mn ions eluted from the positive electrode active material are trapped (captured) in a route leading to the negative electrode active material. And in order to capture | acquire the said Mn ion, it discovered that the fall of battery capacity was actually suppressed by arrange | positioning the polymer containing an acidic functional group between both active materials, and completed this invention.

One invention disclosed herein relates to a lithium ion secondary battery. The lithium ion secondary battery includes a positive electrode having a positive electrode active material containing manganese (eg, spinel type lithium manganese oxide) and a negative electrode having a negative electrode active material. The battery includes an electrolyte (typically a non-aqueous electrolyte) interposed between the positive electrode and the negative electrode. The battery further includes an acidic group-containing polymer disposed between the positive electrode active material and the negative electrode active material.

According to the lithium ion secondary battery having such a configuration, Mn ions that can be eluted from the positive electrode active material are captured using the acidic groups (for example, —COOH group, —SO ₃ H group, etc.) of the acidic group-containing polymer. can do. Therefore, the event that the eluted Mn forms a high-resistance film on the negative electrode can be prevented or suppressed.

In this specification, “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of lithium ions between the positive and negative electrodes. The technology disclosed herein is typically applied to a lithium ion secondary battery in a form that does not use metallic lithium (single element) as an electrode constituent material.

Favorable examples of the acidic group-containing polymer include a polymer (for example, polyacrylic acid) containing at least one of acrylic acid and methacrylic acid as a monomer composition. It may be a homopolymer of acrylic acid or methacrylic acid, or a copolymer with other monomers. An example of a preferable acidic group-containing polymer is polyacrylic acid.

The acidic group-containing polymer can be arranged, for example, by removing the solvent from a solution obtained by dissolving the polymer in a suitable solvent (for example, drying the solution). As the solvent, an organic solvent (for example, a lower alcohol such as ethyl alcohol) can be preferably used. By removing the solvent from the organic solvent solution and disposing the acidic group-containing polymer, a lithium ion secondary battery exhibiting higher charge / discharge cycle characteristics can be realized.

As the position where the acidic group-containing polymer is disposed, a portion that does not directly contact the positive electrode can be preferably selected. Arranging at such a position is advantageous in preventing an event that the acidic group-containing polymer is altered by the high potential of the positive electrode. Therefore, a lithium ion secondary battery having better durability against charge / discharge cycles can be realized.

The negative electrode of the lithium ion secondary battery disclosed herein typically includes a negative electrode mixture layer containing the negative electrode active material. In a preferred embodiment, the acidic group-containing polymer is disposed on the negative electrode mixture layer. A battery having such a configuration can be preferably manufactured by, for example, applying the acidic group-containing polymer solution to the surface of the negative electrode mixture layer and drying it. The amount of the acidic group-containing polymer disposed per 1 cm ² of the area of the negative electrode mixture layer can be, for example, about 0.01 mg to 0.20 mg.

Another invention disclosed herein is a positive electrode having a positive electrode active material containing manganese, a negative electrode having a negative electrode mixture layer containing a negative electrode active material, and an electrolyte interposed between the positive electrode and the negative electrode. The present invention relates to a method of manufacturing a lithium ion secondary battery comprising (typically a non-aqueous electrolyte) and an acidic group-containing polymer disposed on the negative electrode mixture layer. The method includes a step of applying an organic solvent solution of the acidic group-containing polymer to the negative electrode mixture layer and then removing the organic solvent and placing the polymer on the negative electrode mixture layer. Further, the method may include a step of building a battery by housing the negative electrode on which the polymer is disposed and the positive electrode together with the electrolyte in a container. According to this method, it is possible to appropriately manufacture a lithium ion secondary battery that exhibits better charge / discharge cycle characteristics while having a configuration including a positive electrode active material containing Mn.

The lithium ion secondary battery disclosed herein is suitable as a secondary battery mounted on a vehicle because it is excellent in charge / discharge cycle characteristics as described above. For example, it can be suitably used as a power source for a motor (electric motor) of a vehicle such as an automobile. Therefore, according to the present invention, there is provided a vehicle including any lithium ion secondary battery disclosed herein (which may be a battery manufactured by any method disclosed herein).

FIG. 1 is a partial cross-sectional perspective view schematically showing a configuration of a lithium ion secondary battery according to an embodiment. FIG. 2 is a schematic cross-sectional view showing a positive and negative electrode sheet and a separator constituting a secondary battery according to an embodiment. FIG. 3 is a schematic cross-sectional view showing positive and negative electrode sheets and a separator constituting a secondary battery according to another embodiment. FIG. 4 is a side view schematically showing a vehicle (automobile) including the secondary battery according to the embodiment.

Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

The technology disclosed herein can be applied to various forms of lithium ion secondary batteries constructed using a positive electrode including a positive electrode active material containing Mn (a Mn-containing positive electrode active material). The Mn-containing positive electrode active material can be, for example, a manganese compound having a crystal structure such as a spinel type, a layered rock salt type, or an olivine type.

A typical example of the Mn-containing positive electrode active material is lithium manganese oxide having a spinel crystal structure. Examples of this type of lithium manganese oxide include LiMn ₂ O ₄ and compounds having a composition in which part of the Mn is replaced with another metal element (lithium manganese oxide having a partially substituted spinel structure). . For example, a spinel compound represented by the general formula: LiM _y Mn _2-y O ₄ ; can be preferably used as the positive electrode active material in the technology disclosed herein. Y in the general formula is typically a number satisfying 0 ≦ y ≦ 0.7, and preferably 0.4 ≦ y ≦ 0.6. In the case of 0 <y, M in the above general formula is a kind selected from Li, Mg, Al, Ni, Fe, Co, Cr, Cu, Be, B, Na, K, Ca, Si, Ge, and Ti. Or it can be two or more. An oxide having a composition in which 50% or more of a metal element other than lithium is Mn in terms of the number of atoms is preferable. One specific example is LiNi _0.5 Mn _1.5 O ₄ .

Another example of the Mn-containing positive electrode active material is lithium manganese oxide having a layered rock salt type crystal structure. As this type of lithium manganese oxide, in addition to LiMnO ₂ , a part of the Mn is selected from other metal elements (for example, Li, Mg, Al, Ni, Fe, Co, Ti, Zr, Nb). Or the compound of the composition replaced by 2 or more types is illustrated. An oxide having a composition in which 50% or more of a metal element other than lithium is Mn in terms of the number of atoms is preferable. Specific examples include LiNi _0.5 Mn _0.5 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li _4/3 Mn _2/3 O _{2 and the} like.

Another example of the Mn-containing positive electrode active material is lithium manganese oxide having an olivine type crystal structure. For example, use of an olivine type compound represented by the general formula: LiM _x Mn _1-x ZO ₄ ; is preferable. Z in the above general formula may be P and / or Si. x is typically a number that satisfies 0 ≦ x ≦ 0.6, and preferably 0 ≦ x ≦ 0.5. When 0 <x, M in the above general formula may be one or more selected from Fe, Mg, Ni, and Co. Specific examples include LiMnPO ₄ , LiFe _0.1 Mn _0.9 PO _{4 and the} like.

As such a Mn-containing positive electrode active material (typically in particulate form), for example, lithium manganese oxide powder prepared and provided by a conventionally known method can be used as it is. For example, a lithium manganese oxide powder substantially composed of secondary particles having an average particle size in the range of about 1 μm to 25 μm (typically about 2 μm to 15 μm) is used as the positive electrode active in the technology disclosed herein. It can preferably be employed as a substance.

As a typical form of a positive electrode having such an active material, a positive electrode mixture containing the active material (typically including the active material as a main component, that is, a component occupying 50% by mass or more) is a current collector. The form held in is mentioned. As a constituent material of the current collector (positive electrode current collector), a conductive metal material such as aluminum can be preferably employed as in the conventional general lithium ion secondary battery. The shape of the current collector is not particularly limited, and may be, for example, a rod shape, a plate shape, a sheet shape, a foil shape, a mesh shape, or the like. Preferable examples of the positive electrode in the technology disclosed herein include a positive electrode in a form in which a positive electrode mixture layer is provided on one or both sides of a sheet-like or foil-like current collector.

The positive electrode mixture may contain a conductive material, a binder (binder), and the like as necessary in addition to the positive electrode active material. As the conductive material, a carbon material such as carbon black (for example, acetylene black) or graphite powder can be preferably used as in the case of a conductive material in an electrode of a general lithium ion secondary battery. As the binder, polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), or the like can be used. Although not particularly limited, the amount of the conductive material used relative to 100 parts by mass of the positive electrode active material can be, for example, 1 to 20 parts by mass (preferably 5 to 15 parts by mass). Further, the amount of the binder used relative to 100 parts by mass of the positive electrode active material can be, for example, 0.5 to 10 parts by mass.

The positive electrode mixture layer is, for example, a composition (typically a paste or slurry) in which a positive electrode active material and a conductive material used as necessary are dispersed in a liquid medium containing an appropriate solvent and a binder. The composition is preferably applied to a current collector, dried and optionally pressed. As the solvent, any of water, an organic solvent and a mixed solvent thereof can be used.

As the negative electrode active material in the technology disclosed herein, an appropriate material can be adopted from various materials that are generally known to function as a negative electrode active material of a lithium ion secondary battery. As a suitable active material, a particulate carbon material (carbon particles) including a graphite structure (layered structure) at least partially may be mentioned. The property (outer shape) of the negative electrode active material is preferably particulate. For example, carbon particles having an average particle diameter of about 5 μm to 50 μm can be preferably used.

As a typical form of the negative electrode having such an active material, a negative electrode mixture containing the active material (typically including the active material as a main component, that is, a component occupying 50% by mass or more) is a current collector. The form held in is mentioned. As a constituent material of the current collector (negative electrode current collector), a conductive metal material such as copper can be preferably employed as in the case of a conventional general lithium ion secondary battery. The shape of the current collector may be various shapes such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape, similar to the positive electrode side. Preferable examples include a negative electrode in a form in which a negative electrode mixture layer is provided on one side or both sides of a sheet-like or foil-like current collector.

The negative electrode mixture may contain a negative electrode active material, a conductive material similar to the positive electrode side, a binder, and the like as necessary. Although not particularly limited, the amount of the binder used relative to 100 parts by mass of the negative electrode active material can be, for example, 0.5 to 10 parts by mass. Similarly to the positive electrode side, the negative electrode mixture layer is prepared by applying a composition in which the negative electrode active material is dispersed in a liquid medium containing an appropriate solvent and a binder to a current collector, drying it, and pressing it as desired. Preferably it can be made.

As the electrolyte interposed between the positive electrode and the negative electrode, a liquid electrolyte (nonaqueous electrolyte) containing a nonaqueous solvent and a lithium salt (supporting electrolyte) soluble in the solvent can be preferably used. The electrolyte may be a solid (gel) electrolyte in which a polymer is added to the electrolyte. The non-aqueous solvent is selected from non-aqueous solvents that are generally known to be usable for electrolytes of lithium ion secondary batteries, such as carbonates, esters, ethers, nitriles, sulfones, and lactones. 1 type, or 2 or more types can be used.

Examples of the supporting electrolyte include LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (SO ₂ CF ₃ ₃ ), LiClO ₄ or the like, one or more selected from various lithium salts known to be capable of functioning as a supporting electrolyte for lithium ion secondary batteries can be used. The concentration of the supporting electrolyte (supporting salt) is not particularly limited, and can be, for example, the same level as that of a conventional lithium ion secondary battery. Usually, a nonaqueous electrolytic solution containing a supporting electrolyte at a concentration of about 0.1 mol / L to 5 mol / L (for example, about 0.8 mol / L to 1.5 mol / L) can be preferably used.

In a preferred embodiment of the lithium ion secondary battery disclosed herein, an electrode body (rolled electrode body) formed by stacking and winding a sheet-like positive electrode and a negative electrode is housed in a container together with a non-aqueous electrolyte. ing. The shape (outer shape of the container) of the lithium ion secondary battery is not particularly limited, and may be, for example, a cylindrical shape, a square shape, a coin shape, or the like.

In a preferred embodiment, a separator is interposed between the positive electrode and the negative electrode. As a separator, the thing similar to the separator used for a general lithium ion secondary battery can be used, and it does not specifically limit. For example, a porous sheet made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide, a nonwoven fabric, or the like can be used. Note that in a lithium ion secondary battery using a solid electrolyte, the electrolyte may also serve as a separator.

The lithium ion secondary battery disclosed herein has an acidic group-containing polymer disposed between the positive electrode active material and the negative electrode active material. The acidic group (acidic functional group) of the polymer can be, for example, one or both of a carboxyl group (—COOH) and a sulfonic acid group (—SO ₃ H). For example, a polymer in which the acidic group is substantially only a carboxyl group is preferable. Such an acidic group-containing polymer is typically a polymer having a monomer composition including a monomer having an acidic group (acidic group-containing monomer).

A typical example of the acidic group-containing monomer includes a compound having a carboxyl group and an ethylenically unsaturated group in one molecule. The ethylenically unsaturated group may be an acryloyl group, a methacryloyl group, a vinyl group, an allyl group, or the like. Specific examples of such compounds include monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; dicarboxylic acids such as maleic acid, itaconic acid, and citraconic acid; and the like. Examples of preferred acidic group-containing monomers include acrylic acid and methacrylic acid. Among these, an acidic group-containing polymer having a monomer composition containing acrylic acid is preferable.

The acidic group-containing polymer may be a polymer having a monomer composition consisting of only one or two or more acidic group-containing monomers, and may be an acidic group-containing monomer and another monomer (that is, having no acidic group). A copolymer may also be used. As such other monomers, various compounds copolymerizable with acidic group-containing monomers can be used. A compound having an ethylenically unsaturated group is preferable, and a compound having an acryloyl group or a methacryloyl group (particularly an acryloyl group) is particularly preferable. Or the acidic group containing polymer of the monomer composition which does not contain the monomer which does not have an acidic group substantially may be sufficient.

In a preferred embodiment of the acidic group-containing polymer in the technology disclosed herein, 50 to 100% by mass (more preferably 75 to 100% by mass, for example 90 to 100% by mass) of the monomer composition is the acidic group-containing monomer. . If the polymerization ratio of the acidic group-containing monomer is too small, the Mn ion trapping performance of the acidic group-containing polymer may be lowered, and the effect of improving charge / discharge cycle characteristics by the polymer may not be sufficiently exhibited.

Such an acidic group-containing polymer can be easily produced by a conventionally known method, or a commercially available product can be easily obtained. Usually, it is appropriate to use an acidic group-containing polymer having a weight average molecular weight (Mw) of 100 × 10 ⁴ or less. For example, a polymer having an Mw of 50 × 10 ⁴ or less can be preferably used. If the Mw is too high, when the polymer is placed by removing the solvent from the solvent solution of the acidic group-containing polymer, there is a disadvantage that the polymer becomes difficult to dissolve in the solvent or the viscosity of the polymer solution becomes too high. There may be cases. The Mw of the acidic group-containing polymer is preferably 1 × 10 ⁴ or more, and more preferably 2 × 10 ⁴ or more (for example, 5 × 10 ⁴ or more). If Mw is too low, part or all of the acidic group-containing polymer may be easily moved (lost) from the initial arrangement position due to stress or the like that may be applied during the production or use of the battery.

The acidic group-containing polymer may be disposed at a location where Mn ions eluted from the positive electrode active material can capture the Mn ions in the route to the negative electrode active material. In order to efficiently capture Mn ions while suppressing an increase in internal resistance, the acidic group-containing polymer is preferably arranged in a thinly spread form (for example, a film form, a sheet form, or the like). For example, the surface of the positive electrode mixture layer and / or the negative electrode mixture layer that faces the counter electrode mixture layer, the surface of the separator that faces the positive electrode mixture layer and / or the negative electrode mixture layer in the configuration having the separator The acidic group-containing polymer can be disposed at the location by applying a solution of the acidic group-containing polymer to the surface or the like on the side facing the substrate and drying it. Alternatively, a sheet (which may be non-porous or porous) formed with an acidic group-containing polymer is interposed between the positive electrode and the negative electrode (in the configuration having a separator, between the positive electrode and the separator and And / or between the negative electrode and the separator).

In a preferred embodiment, an acidic group-containing polymer is disposed at a location that does not directly contact the positive electrode. This is advantageous in preventing an event in which the acidic group-containing polymer is denatured (can be cross-linked, decomposed, functional group converted, etc.) due to the high potential of the positive electrode. For example, in an aspect in which the acidic group-containing polymer is disposed on the surface of the negative electrode mixture layer, a configuration having a separator, an aspect in which the acidic group-containing polymer is disposed on the surface facing the negative electrode mixture layer, between the negative electrode and the separator A configuration in which a sheet of an acidic group-containing polymer is disposed can be preferably employed.

As a method of disposing an acidic group-containing polymer on the surface of the negative electrode mixture layer, the solvent is removed from a solution (polymer solution) in which the polymer is dissolved or uniformly dispersed in an appropriate solvent (for example, the solution is dried). Method) can be preferably employed. As the solvent, any of water, an organic solvent, and a mixed solvent thereof can be used. In a preferred embodiment, the polymer is arranged using a solution containing an acidic group-containing polymer in a solvent containing an organic solvent. Thereby, a lithium ion secondary battery having more excellent charge / discharge cycle characteristics can be realized. The solvent containing the organic solvent is a solvent composed of only one or two or more organic solvents, or a mixed solvent of an organic solvent and water (typically, the organic solvent is a main component, that is, occupies 50% by volume or more. Solvent as a component). Examples of the organic solvent include lower alcohols having about 1 to 4 carbon atoms, acetone, tetrahydrofuran, N-methylpyrrolidone, and acetic acid esters (typically esters of lower alcohols having about 1 to 4 carbon atoms and acetic acid such as ethyl acetate. ), Carbonate ester and the like can be appropriately selected and used. Examples of preferable organic solvents include methyl alcohol, ethyl alcohol, isopropyl alcohol and the like.

For example, by applying such a polymer solution to the surface of the negative electrode mixture layer and drying, the acidic group-containing polymer is disposed on the negative electrode mixture layer (in other words, the surface of the negative electrode mixture layer is acidic. Group-containing polymer). As a method for applying the polymer solution, a method using a coating machine such as a slit coater, a method of immersing the negative electrode mixture layer in the polymer solution (dip coating), and a method of spraying the polymer solution on the surface of the negative electrode mixture layer (spray coating) ), Etc., can be employed as appropriate. In this way, by applying the polymer solution to the surface of the negative electrode mixture layer formed in advance, the acidic group-containing polymer is concentrated (is unevenly distributed) in the negative electrode where the Mn ions first reach. be able to. According to such a configuration, for example, Mn ions can be efficiently captured by a smaller amount of polymer as compared with a configuration in which the acidic group-containing polymer is uniformly arranged up to the inside of the negative electrode mixture layer. Therefore, it is possible to effectively improve the charge / discharge cycle characteristics while suppressing adverse effects (for example, increase in internal resistance) that may occur due to the arrangement of the acidic group-containing polymer. In addition, in a battery including a negative electrode having a configuration in which another layer (for example, a porous ceramic layer) is formed on the negative electrode mixture layer, an acidic group-containing polymer may be disposed on the surface of the layer.

In the lithium ion secondary battery in which the acidic group-containing polymer is arranged on the negative electrode mixture layer, the amount of the polymer arranged is usually 1.00 mg or less per 1 cm ^{2 of the} negative electrode mixture layer area (formation area) ( that 1.00 mg / cm ² or less) and it is appropriate to, 0.50 mg / cm ² or less (more preferably 0.20 mg / cm ² or less, typically 0.20 mg / cm less than ^2, for example 0 .18 mg / cm ² or less). If the amount is too large, the polymer may hinder material exchange between the negative electrode mixture layer and the outside (for example, movement of lithium ions or electrolyte), and battery performance may tend to be reduced. The lower limit of the arrangement amount of the acidic group-containing polymer is not particularly limited. In order to exhibit the effect of arranging the polymer well, it is usually appropriate that the amount of the polymer is 0.01 mg / cm ² or more, and preferably 0.03 mg / cm ² or more. . In addition, in the aspect by which the acidic group containing polymer was arrange | positioned at the negative electrode compound-material layer side surface of a separator, it is good to make the polymer arrangement amount per 1 cm < ² > of a separator into the said range.

Hereinafter, an embodiment of the lithium ion secondary battery disclosed herein will be described with reference to the drawings. As shown in FIG. 1, a lithium ion secondary battery 10 includes a battery case (container) having a shape in which an electrode body 11 including a positive electrode 12 and a negative electrode 14 can accommodate the electrode body together with a non-aqueous electrolyte solution 20. 15. At least a part of the nonaqueous electrolytic solution 20 is impregnated in the electrode body 11.

The electrode body 11 includes a positive electrode (positive electrode sheet) 12 having a structure in which a positive electrode mixture layer 124 including a positive electrode active material is provided on a long sheet-like positive electrode current collector 122 and a negative electrode mixture layer including a negative electrode active material. A negative electrode (negative electrode sheet) 14 having a configuration in which 144 is provided on a long sheet-like negative electrode current collector 142 is superposed on two long sheet-like separators 13, and these are wound into a cylindrical shape. Is formed.

The battery case 15 includes a bottomed cylindrical case main body 152 and a lid 154 that closes the opening. The lid 154 and the case main body 152 are both made of metal and insulated from each other, and are electrically connected to the positive and negative

current collectors

122 and 142, respectively. That is, in the lithium ion secondary battery 10, the lid body 154 also serves as a positive electrode terminal, and the case body 152 serves as a negative electrode terminal.

On one edge along the longitudinal direction of the positive electrode current collector 122, a portion where the current collector 122 is exposed without providing the positive electrode mixture layer (positive electrode mixture layer non-forming portion) is provided. Similarly, on one edge along the longitudinal direction of the negative electrode current collector 142, a portion where the current collector 142 is exposed without the negative electrode mixture layer (a negative electrode mixture layer non-forming portion) is provided. . The lid 154 and the case main body 152 are connected to the exposed portions.

As shown in FIG. 2, an acidic group-containing polymer (for example, polyacrylic acid) 18 is disposed on the negative electrode mixture layer 144 constituting the negative electrode sheet 14. Thus, the electrode body 11 is formed by overlapping and winding the negative electrode sheet 14 coated with the acidic group-containing polymer 18 with another member. 2 illustrates a configuration in which the polymer 18 is disposed on the entire surface of the negative electrode mixture layer 144 provided on both surfaces of the negative electrode current collector 142, but the negative electrode mixture provided on one surface is illustrated. The polymer 18 may be disposed only on the layer 144, or the polymer 18 may be disposed only on a partial area of the surface. Alternatively, as in the modification shown in FIG. 3, the acidic group-containing polymer 18 is disposed on the surface of the separator 13 on the negative electrode mixture layer 144 side, and the separator 13 thus coated with the acidic group-containing polymer 18 is used as another member. The electrode body 11 may be formed by overlapping and winding.

The technology disclosed herein is a charge / discharge condition in which the upper limit voltage between terminals can be 4.5 V or higher (for example, 4.7 V or higher, particularly 4.8 V or higher, typically 7 V or lower, for example, 5.5 V or lower). It can be preferably applied to a lithium ion secondary battery for use in the above. As a suitable example of such a battery, a so-called 5V class lithium ion secondary battery provided with a spinel type lithium manganese oxide as a positive electrode active material can be mentioned. The matter disclosed by this specification includes any lithium ion secondary battery disclosed herein (preferably, a secondary battery including spinel type lithium manganese oxide as a positive electrode active material) having an upper limit voltage. A method of using the battery under charge / discharge conditions that can be 4.5 V or higher (for example, 4.7 V or higher, particularly 4.8 V or higher, typically 7 V or lower, for example, 5.5 V or lower); And a mechanism for controlling the battery under charge / discharge conditions set so as to be the upper limit voltage, and a vehicle equipped with the power supply system.

Hereinafter, some examples relating to the present invention will be described. However, the present invention is not intended to be limited to the specific examples.

<Example 1>
As the positive electrode active material, lithium manganese oxide having a composition represented by LiNi _0.5 Mn _1.5 O ₄ was used. To a solution obtained by dissolving 25 g of polyvinylidene fluoride (PVDF) as a binder in 625 mL of N-methylpyrrolidone (NMP), 425 g of lithium manganese oxide powder having the above composition and 50 g of acetylene black were added and mixed uniformly. A paste or slurry composition (a composition for forming a positive electrode mixture layer) was prepared. This composition was applied to both sides of a 15 μm thick long aluminum foil (positive electrode current collector) and dried. The coating amount (solid content basis) of the above composition was adjusted to be about 15 mg / cm ^{2 on} both sides. After drying, pressing was performed so that the total thickness of the positive electrode current collector and the positive electrode mixture layers on both sides thereof was about 70 μm, thereby preparing a sheet-like positive electrode (positive electrode sheet).

462.5 g of graphite powder was put into a solution obtained by dissolving 37.8 g of PVDF in 625 mL of NMP, and mixed uniformly to prepare a paste or slurry-like composition (a composition for forming a negative electrode mixture layer). . This composition was applied to both sides of a long copper foil (negative electrode current collector) having a thickness of 10 μm and dried. The coating amount (solid content basis) of the composition was adjusted to be about 9 mg / cm ^{2 on} both sides. After drying, the whole thickness was pressed to about 70 μm to produce a sheet-like negative electrode (negative electrode sheet).

The negative electrode sheet (without polymer coating) was laminated with the positive electrode sheet and two long separator sheets, and the laminate was wound in the long direction to produce a wound electrode body. As the separator sheet, a porous polyethylene sheet having a thickness of 25 μm was used. The electrode body was used together with an electrolytic solution (an electrolytic solution having a composition in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a solvent in which EC and DEC were mixed at a volume ratio of 3: 7). The 18650 type lithium ion secondary battery (battery sample 1) was constructed.

<Example 2>
The negative electrode sheet produced in Example 1 is immersed in a 2.5 mass% ethyl alcohol solution of polyacrylic acid (weight average molecular weight 25 × 10 ⁴ ) for about 5 seconds, and then pulled up from the solution and dried under reduced pressure at 120 ° C. Thus, the surface of the negative electrode mixture layer was coated with polyacrylic acid. The coating amount of polyacrylic acid calculated from the mass difference before and after the coating and the area of the negative electrode mixture layer was 0.15 mg (that is, 0.15 mg / cm ² ) per 1 cm ² of the area of the negative electrode mixture layer. A battery sample 2 was constructed in the same manner as in Example 1 except that a negative electrode sheet coated with polyacrylic acid was used.

<Example 3>
In Example 2, the polyacrylic acid concentration in the polyacrylic acid ethyl alcohol solution was changed to 1.0 mass%. The other points were the same as in Example 2, and the negative electrode mixture layer was coated with polyacrylic acid. The coating amount was 0.10 mg / cm ² . A battery sample 3 was constructed in the same manner as in Example 1 except that the negative electrode sheet coated with polyacrylic acid was used.

<Example 4>
In Example 2, instead of a 2.5% by mass ethyl alcohol solution of polyacrylic acid, a 2.5% by mass aqueous solution of polyacrylic acid was used. The other points were the same as in Example 2, and the negative electrode mixture layer was coated with polyacrylic acid. The coating amount was 0.10 mg / cm ² . A battery sample 4 was constructed in the same manner as in Example 1 except that the negative electrode sheet coated with polyacrylic acid was used.

<Example 5>
In Example 2, instead of the 2.5 mass% ethyl alcohol solution of polyacrylic acid, a 2.5 mass% toluene solution of polyacrylic acid (weight average molecular weight 25 × 10 ⁴ ) was used. The other points were the same as in Example 2, and the negative electrode mixture layer was coated with polyethyl acrylate. The coating amount was 0.10 mg / cm ² . A battery sample 5 was constructed in the same manner as in Example 1 except that a negative electrode sheet coated with polyethyl acrylate was used.

<Example 6>
In Example 2, instead of a 2.5% by mass ethyl alcohol solution of polyacrylic acid, a 2.5% by mass aqueous solution of sodium polyacrylate (degree of polymerization 22 × 10 ³ to 70 × 10 ³ ) was used. The other points were the same as in Example 2, and the negative electrode mixture layer was coated with sodium polyacrylate. The coating amount was 0.10 mg / cm ² . A battery sample 6 was constructed in the same manner as in Example 1 except that a negative electrode sheet coated with sodium polyacrylate was used.

<Example 7>
In this example, lithium nickel oxide having a composition represented by LiNi _0.8 Co _0.15 Al _0.05 O ₄ was used as the positive electrode active material. Using this lithium nickel oxide powder, a composition for forming a positive electrode mixture layer was prepared in the same manner as in Example 1, and applied to both sides of a 15 μm-thick long aluminum foil (positive electrode current collector) and dried. It was. The coating amount (based on solid content) of the composition was adjusted to be about 13 mg / cm ^{2 on} both sides. After drying, the positive electrode current collector and the positive electrode mixture layers on both sides thereof were pressed to a total thickness of about 65 μm to produce a sheet-like positive electrode (positive electrode sheet). This positive electrode sheet was laminated with a negative electrode sheet (without polymer coating) and two long separator sheets, and a battery sample 7 was constructed in the same manner as in Example 1.

<Example 8>
In this example, the positive electrode sheet of Example 7 and the polyacrylic acid-coated negative electrode sheet of Example 2 were used in combination. The battery sample 8 was constructed in the same manner as Example 1 for the other points.

The characteristics of the battery samples 1 to 8 obtained above were evaluated as follows. The obtained results are shown in Table 1 together with the schematic configuration of each battery sample.

[Initial discharge capacity measurement]
For each battery sample, the voltage between both terminals was 4.9 V at a rate of 0.1 C of theoretical capacity (1 C is a current value that can be fully charged and discharged in 1 hour) (however, 4 for battery samples 7 and 8). .1V), and the operation of constant current discharge at 0.1 C until the voltage between both terminals reached 3.0 V was performed for 3 cycles. Next, constant current charging to 4.9 V (4.1 V for battery samples 7 and 8) at a rate of 1 C, followed by constant voltage charging until the total charging time is 2 hours, then 3. A constant current was discharged to 0 V, and the capacity at this time was measured as the initial discharge capacity (mAh). In addition, the above operation was performed at 25 degreeC.

[Cycle characteristics evaluation]
The battery sample after measurement of the initial discharge capacity is charged at a constant current up to 4.9 V (4.1 V for battery samples 7 and 8) at a rate of 1 C, and then charged at a constant voltage until the total charging time is 2 hours. The operation and the operation of discharging a constant current to 3.0 V at a rate of 1 C were performed 100 cycles. The above operation was performed at 25 ° C. And the ratio of the discharge capacity of the 100th cycle with respect to the discharge capacity of the 1st cycle was computed as a capacity | capacitance maintenance factor.

As can be seen from this table, out of the battery samples 1 to 6 provided with the Mn-containing positive electrode active material, the samples 2 to 4 in which the negative electrode mixture layer was coated with polyacrylic acid had a capacity compared to the sample 1 in which the polymer was not coated. Maintenance rate improved. Especially, according to the samples 2 and 3 using the ethyl alcohol solution of polyacrylic acid for the coating, a clearly higher capacity retention rate was realized as compared with the sample 4 using the aqueous solution. In particular, in Sample 2, the capacity retention rate was improved by 10% or more compared to Sample 1 in which the polymer was not coated. In Sample 4 using an aqueous solution, although the capacity retention rate was improved, the initial capacity was reduced, whereas in Samples 2 and 3 using an ethyl alcohol solution, an initial capacity almost equal to that of Sample 1 was maintained.

On the other hand, in the sample 5 coated with the homopolymer of ethyl acrylate having no acidic functional group, the effect of improving the capacity retention rate was not observed. In sample 6 coated with polyacrylate instead of polyacrylic acid, the capacity retention rate was slightly lower than that of sample 1, and the initial capacity was also reduced. In Example 2, when the coating amount of polyacrylic acid was 0.20 mg / cm ² , both the capacity retention ratio and the initial capacity were lower than those of Sample 1. Also, when the same polyacrylic acid ethyl alcohol solution as in Example 2 was coated on the surface of the positive electrode mixture layer instead of the surface of the negative electrode mixture layer, a battery sample was produced in the same manner. There was no improvement.

On the other hand, as can be seen from the comparison of the battery samples 7 and 8, in the battery using the positive electrode active material not containing Mn, the effect of improving the charge / discharge cycle characteristics by covering with the acidic group-containing polymer was not observed. This is presumably because a battery using a positive electrode active material not containing Mn does not have a problem of deterioration in charge / discharge cycle characteristics due to elution of Mn ions. In addition, when the battery sample 1 was decomposed | disassembled after the said cycle characteristic evaluation test and the negative electrode surface was analyzed by the inductively coupled plasma (IPC) emission-spectral-analysis method, presence of Mn was confirmed. This result shows that in the battery sample 1, the elution of Mn ions and the deposition on the negative electrode occurred in the cycle characteristic evaluation test.

Although the present invention has been described in detail above, the above embodiment is merely an example, and the invention disclosed herein includes various modifications and changes of the above specific examples.

Since the lithium ion secondary battery provided by the technology disclosed herein exhibits excellent performance (such as charge / discharge cycle characteristics) as described above, it can be used as a lithium ion secondary battery for various applications. . For example, it can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Such lithium ion secondary batteries may be used in the form of an assembled battery formed by connecting a plurality of them in series and / or in parallel. Therefore, according to the technology disclosed herein, as schematically shown in FIG. 4, a vehicle (typically, an automobile) including such a lithium ion secondary battery (which may be in the form of an assembled battery) 100 as a power source. In particular, a vehicle (1) equipped with an electric motor such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle can be provided.

Claims

A positive electrode having a positive electrode active material containing manganese;
A negative electrode having a negative electrode active material;
A non-aqueous electrolyte interposed between the positive electrode and the negative electrode;
An acidic group-containing polymer disposed between the positive electrode active material and the negative electrode active material;
A lithium ion secondary battery comprising:
The battery according to claim 1, wherein the polymer is a polymer containing at least one of acrylic acid and methacrylic acid as a monomer composition.
The battery according to claim 1 or 2, wherein the polymer is polyacrylic acid.
The battery according to any one of claims 1 to 3, wherein the polymer is disposed by removing the organic solvent from an organic solvent solution of the polymer.
The battery according to any one of claims 1 to 4, wherein the polymer is disposed at a location that does not directly contact the positive electrode.
The battery according to any one of claims 1 to 5, wherein the negative electrode includes a negative electrode mixture layer including the negative electrode active material, and the polymer is disposed on the negative electrode mixture layer.
The battery according to claim 6, wherein 0.01 mg to 0.20 mg of the polymer is disposed per 1 cm 2 of the area of the negative electrode mixture layer.
The battery according to any one of claims 1 to 7, wherein the positive electrode active material is a spinel type lithium manganese oxide.
A positive electrode having a positive electrode active material containing manganese, a negative electrode having a negative electrode mixture layer containing a negative electrode active material, a non-aqueous electrolyte interposed between the positive electrode and the negative electrode, and the negative electrode mixture layer A method of producing a lithium ion secondary battery comprising: an acidic group-containing polymer disposed;
After applying the organic solvent solution of the polymer to the negative electrode mixture layer, removing the organic solvent and placing the polymer on the negative electrode mixture layer;
Storing a negative electrode in which the polymer is disposed and the positive electrode together with the electrolyte in a container to construct a battery;
A method for producing a lithium ion secondary battery.
A vehicle comprising the lithium ion secondary battery according to any one of claims 1 to 8.